Compositions of matter for the electroplating of cadmium



n wd a Perm 2,892,761 COMPOSITIONS OF MATTER FOR ELECTRG PLATING F CADMIUM William F. Hamilton, Altadena, and Simon, Los

Angeles, Calif., assignors to Lockheed Aircraft Corporation, Burbank, Calif.

No Drawing. Application February 29, 1956 Serial No. 568,944

18 Claims. C1. z'otsli) The present invention is concerned with the plating of metal and has more particular reference to the electrodeposition of cadmium on ferrous metals.

In the construction of airframes, modern light-weight machinery, and in other situations, it is desirable or essential that the primary structures be as light in weight and as strong as possible. This is often accomplished by fabricating or constructing the member subject to heavy loads and stresses of high-strength steels. For example, ferrous alloys having ultimate strengths in the range of from 260,000 to 280,000 pounds per square inch are frequently employed in the fabrication of aircraft members and elements such as landing gear parts, bolts for the attachment of fuel tanks to wing tips,- wing and empennage parts, motor mounts, and the like. In practice, the weight saving effected by the employment of such high-strength ferrous alloys oftentimes amounts to several hundred pounds in a given large airframe. An important disadvantage attaching to the use of these high-strength ferrous alloys is their susceptibility to rusting and as a consequence the parts and members constructed of these alloys are cadmium plated wherever possible or practical. The cadmium plating not only covers the exposed ferrous alloy surfaces but also provides anodic protection against corrosion should the plating become marred or scratched. Cadmium plating is preferred'in such situations since paints, lacqiier's, organic coatings in general, and nickel, as well as chrominum plating, fail to provide this type of anodic protection.

Cadmium plating of the high-strength ferrous alloys in conventional cyanide solutions is usually attended by the evolution of hydrogen as the metal is being plated and the hydrogen has the effect of embrittling the steel. Baking of the parts subsequent to the plating operation will, in some cases, relieve the embrittlement but willnot always do so. It is possible to cadmium plate the highstrength ferrous alloy parts in plating baths where aqueous cadmium fluoborate is employed, although such parts can become embrittled when baked. Because detection of embrittlement involves destruction of the tested article it is, accordingly, impossible to demonstrate whether embrittlement has affected a given part prior to its actual use. A member or part of high strength ferrous alloy that has become embrittled during the cadmium plating operation. may unpredictably fail in service when subjected to only relatively small sustained loads. Thus a part constructed of 260-280,000 p.s.i. steel may fail under a sustained load which is a fraction of its calculated ultimate strength.

We have discovered aqueous electroplating bath terms lations or solutions useful in cadmium plating steels and other ferrous metals which, when employed in accordance with our invention prevent or avoid hydregenembrittlement of the parts being plated. It is, therefore, a general object of this invention to provide techniques and solutions for electroplating cadmium on ferrous metal parts which avoid hydrogen embrittlement of the base metal of the parts.

Another object of the invention is to provide solutions useful in electroplating of cadmium which enable the deposition of continuous adherent and dense coatings of cadmium metal while avoiding hydrogen embrittlement of the article upon which the coating is deposited.

It is another object of our invention to provide electr'of plating solutions of the character described composed of readily available materials compatible with the ingredients now commonly employed in the cadmium plating art and which enable the plating operation to be succeSsfully carried out without hydrogen embrittlement of the members or parts being plated. I n

It is another object of this invention to provide modif fied alkali metal cadmicyanide solutions incorporating simple additives or addition ingredients which may be easily controlled during sustained operation of I the plat ing bath, which ingredients result in or assure the forma; tion of adherent, continuous and dense plating without embrittlement of the plated articles.

A further object of this invention is to provide cad-'- rnium electroplating bath formulations and operating conditions effective in depositing satisfactory plate without hydrogen embrittlement of the article plated and which give an added safety factor by providing for the auto matic relief of any embrittlement in air in case it is ac-' cidently incurred.

A further and important objectof our invention is to provide cadmium plating solutions having ample and effective throwing power to assure the deposition of the cadmium metal in the roots of threads, in crevices, and on other irregularities of the parts being plated as well as on surfaces thereof that are otherwise difficult to plate and might otherwise be conducive to rough, discontinuous or irregular plating. In accordance with our invention, nitrate ions are added to a cadmium electroplating solution of high cadmium-low free cyanide content which would normally have poor throwing power and low efiiciency but we have discovered that the inclusion of an alkylamine in the solution or bath increases both the throwing power and the etliciency of the solution to not only reduce the sensitivity of the plating to the prevailing surface conditions but to also impart better plating characteristics to the solution.

These and other objects of our invention will become apparent from the following detailed description.

The non-embrittling aqueous cadmium cyanide electroplating solutions of the invention may be said to comprise, generally, a relatively high percentage of cadmium metal, a relatively low percentage of free cyanide, hydroXide; nitrate ions for preventing or reducing the formation of hydrogen at the cathode and a relatively small amount of a selected alkylamine to increase both the throwing power and the plating etliciency of the bath.

In accordance With the invention cadmium metal is plated from an aqueous cyanide solution which contains a relatively high percentage of cadmium metal and-a relatively low percentage of free cyanide. Nitrate ions added to the solution prevent the formation of hydrog'en at the cathode under ordinary operating conditions and thus efiectively avoid embrittlement of the parts plated in the solution unless an extremely high current density is used. conventionally, however, the addition of even small amounts of nitrate ions to cadmicyanide plating baths is avoided because both the efficiency of the bath and the qualityof the resultant plate are adversely affected thereby. The effect on the efliciency of the bath is minimized in the present invention by reason of the metal content and relatively low cyanide content, high metal content and low cyanide baths being inherently highly efiicient. Another disadvantage of such a high cadmium, low free cyanide bath containing added nitrate is the marked reduction in throwing power. In practice, this means that the solution will fail to properly deposit cadmium metal in the roots of screw threads of bolts, for example, increvices, and on other irregularities of the plated articles and that the sensitivity of the plate to the condition of the surface of the article being plated is extreme and critical. Thus slight films of surface oxide, almost imperceptible grease films, and the like, may make the deposited plate rough, irregular or discontinuous. We have discovered that the disadvantages of the high cadmium-low free cyanide baths containing added nitrate are effectively avoided and practically eliminated by the maintenance in the bath of a small amount of an alkylamine. The amine has been found to increase both the throwing power and the efficiency of the solution and not only reduces the sensitivity of the plating to otherwise critical surface'conditions but also imparts improved plating characteristics to the solution. We have found that proper selection of the added amine enables the production of an excellent fine-grained plate from suitably formulated solutions at current densities varying from less than 1 to more than 100 amperes per square foot. Amperes per square foot will hereinafter be abbreviated a.s.f.

The relative proportions of the ingredients making up the electroplating bath of the invention are subject to considerable variation without increasing embrittlement of the ferrous metal to be plated and while employing a normal range of current densities conventionally utilized in such plating operations. We have found that it' is desirable to maintain the nitrate content of the solution expressed in terms of sodium nitrate between approximately 1% and 6 /2% weight/volume basis or l6 /2 gms./ 100 cc. of plating solution. Where percentage is used herein it is expressed in terms of weight per unit volume except in the case of the throwing power additive. Where the sodium nitrate content is below approximately l% cathodic gassing may occur at usual or normal densities and if the sodium nitrate content is appreciably above about 6.5% the efiiciency of the bath solution may be lower than desirable. The total cadmium metal content of the solution or bath should preferably be between approximately 8% and approximately 15%. It has been noted that if the cadmium metal content is too low, hydrogen embrittlement of the plated metal may be encountered, whereas if the cadmium metal content is excessive, precipitation may occur and drag-out losses may be unnecessarily high.

If desired, potassium salts may be employed instead of the sodium salts within the limits of their solubilities in solutions of this character.

We have found that in a plating solution containing about cadmium metal, the total cyanide content in terms of sodium cyanide should be between 15.5% and 21% and preferably. approximately 20.5%. The free sodium cyanide present in the solution controls the rate of increase of cadmium metal and the total cyanide present governs the total amount of the metal in the solution. In the event the free sodium cyanide exceeds about 3% of the solution, hydrogen embrittlement of the ferrous metal may be induced due to decreased efiiciency of the bath, whereas if the free sodium cyanide content of the bath falls below about 0.1% the quality of the plating may be adversely affected. a Y a As the plating operation progresses, the sodium nitrate is gradually reduced to sodium nitrite and in order to' prevent hydrogen embrittlement of the parts being plated due to local depletion of the nitrate, constant agitation of the bath is desirable. The sodium nitrite concentration of the solution is relatively unimportant since it appears to have little effect either upon hydrogen embrittlement of the parts being plated or upon the quality of the plating.

We prefer to maintain the sodium hydroxide content of the solution or bath between approximately 6% and 8%. However, the concentration of the sodium hydroxide is not believed to be critical. The percentage or concentration of the carbonate present in the solution is also relatively unimportant but in the event it builds up to an excessive value the carbonate may be removed by chilling and filtering solution or by precipitation as an insoluble carbonate.

The above mentioned alkylamine or throwing power additive is employed or required in only a relatively small percentage or concentration. We have found that effect of the relatively small proportion of the throwing power additive is exemplified by employing a solution such as above described without the inclusion of a throwing power additive where we found the initial cathodic plating efliciency of the solution to approximate 10% at 43 a.s.f. This efficiency increased to 50% or more as the solution was employed and the nitrate concentration diminished. We discovered that the addition of approximately 0.5% by volume of a selected throwing power additive, such as n-butylamine to the same solution as initially compounded increased the initial efficiency, that is the initial cathodic plating efiiciency from approximately 10 to approximately The concentration of a given throwing power additive, or given type of additive, may be considered critical since if insufiicient additive is present the plating efliciency of the bath will be low and the distribution of the plate will be uneven whereas if an excessive amount of the additive is present in the solution the bath may produce hydrogen embrittlement of the ferrous metal parts being plated at normal operating current densities. An excess of the additive or amine in addition to producing embrittlement at current densities in the operating range will tend to give a specular plate at high current densities. When employing a preferred or selected throwing power additive such as nbutylamine, n-heptylamine, n-hexylamine, n-amylamine, octylamine or 1-3 diaminobutane, the concentration of the additive should be maintained between approximately 1 and 6 parts per thousand by volume (OJ-0.6% by volume). It is to be understood the amount of additive used in a bath will depend upon the selected additive .the series and may be volatile enough to give rise to excessive evaporation losses. Above a chain length of C5 the effect on the throwing power of the solution is relatively great but hydrogen embrittlement tendency of the ferrous metal being plated also appears to increase at the higher concentrations. We have found that soluble secondary aliphatic amines are effective as throwing power additives for our solutions but may disproportionately increase hydrogen embrittlement. Soluble aromatic alkylamines as well as cyclic amines such as motpholinc, cyclohexylamine and pyridine are excellent in their effect on the throwing power of the solutions but may, in some instances at least, beconducive to excessive hydrogen embrittlement. We have achieved excellent results employing octylamine, n-heptylamin'e, n-hexylamine, n-butylamine, n-amylamine, 1-3 diaminobutane and desoxyephedrine as throwing power additives fonour electroplating solutions... Effective throwing power additives-are ineluded in following Table I; TABLE I Octylamine Diethylamine n-Heptylamine -Aniline n -Hexylarnine Benzylamine n-Amylamine Beta phenylisopr'opylamine n-Butylamine Desoxyephedrine. V Cyclohexylamine n-Aminopropylmorpholine n-Propylamine I 1-3 diaminobutane Other throwing power additives which appear to be effective although less useful than those heretofore set forth are included in following Table II:

, TABLE II Ethylene cyanohydrin Hydroxylamine Lithium nitrate Morpholine Cobaltou's nitrate Pyridine Resorcinol Beta naphthol n-Isobutylamine and dissolved in the water:

, Pounds Sodium cyan 7 77.18 Cadmium oxide 1 i 1 25.6 Cadmium nitrate tetrahydrate, crystal 41.76 Sodium hydr 7.53

The volume of the solution should next be made up to approximately 45 gallons by the addition of distilled or deionized water and the circulating filter operated until the liquid is clear. The throwing power additive may next be added to the, solution, for example in this particular formulation 3-.6 fluid ounces of n-butylamine are added to the solution during constant stirring to minimize evaporation losses. Where conventional cadmium and iron anodes and conventional cathode equipment are employed, thissolution will plate cadmium metal at current densities varying into over 100 a.s.'f. without hydrogen embrittlement of the ferrous metal articles being plated. The cathode efiiciency for the electroplating bath containingn-butylamine additive varies with current ap plied, being greater thanapproximately from 80% at approximately 58 a.s.f. and diminishing at thehigher cur rent densities. The solution will, operate for extended periods of time in normal plating operations. without special or unusual attention or make up being required The electroplating solutions of the invention have the added advantage that should hydrogen embrittlement accidently be increased due to inadvertant use of extremely high current densities, any such embrittlement will be relieved by merely allowing the plated parts to stand in room air for several hours following the plating. Although the plating solution and process of the invention will not cause hydrogen embrittlement of high strength steel parts some of the articles plated may havebecome embrittled during processing prior to the electroplating. For this reason it is advisable to bakeout such high strength plated parts at 'a'temperature of, say, 375 F. for at least eight hours to be assured that the finished parts are not embrittled from any causes.

In making upthe bath or solutions of the invention cadmium metal may be introduced partially as the nitrate and partially as an oxide to reduce the amount of sodium hydroxide formed during the bath makeuphand seats to introduce ilienitrate ions conveniently without unnecessarilyincreasing the sodium ion content. Thus the-so,- dium cyanide may first be dissolved in whereas then the cadmium oxide and cadmiumnitrate added and-dissolved in the solution. The additional sodium hydroxide may be added to the bath at any convenient time. The high cadmium metal content of the solutions increases the current efliciency of the baths and in itself decreases the tendency for hydrogen to form and therefore the tendency for attendant embrittlement of the parts being plated. The low free cyanide content of our solutions has been found to be advantageous from the standpoint of reducing hydrogen em-brittlement. Free sodium cyanide tends to decrease the efiiciency of the plating although some free cyanide is desirable to keep the metal dissolved in the bath and to produce acceptable plating, the low content of the free cyanide is definitely advan- Likewise a small amount-of free sodium hydroxide is apparently required to obtain good metallic deposit although an excess of sodium hydroxide appears to have little elfeet either on the hydrogen embr-ittlement or the quality of the plate.

While we do not intend or wish to be restricted or limited in any way with respect to any particular theory of operation of the solutions of this invention, it appears that the high cadmium-low cyanide solutions give the highly efiective results due to the inherent plating efii ciency which approaches 100% and because the electrical energy introduced into the bath is almost entirely used in depositing the metallic cadmium rather than in forming hydrogen. With the .sodium'nitrate added to the high cadmium low cyanide solution the small amount of electrical energy which might otherwise be expended in form; ing hydrogen is consumed in selectively converting the nitrate to a nitrite with the result that little or no hydrogen is available-or produced to embrittle the metallic parts being plated. I r

The following are typical preferred formulations for the electroplating baths or solutions of the invention.

Example I v Percent w./v. Cadmium metal f I 1'01) Free sodium cyanide 2.0 Totalsodium cyanide 20.5 Sodium hydroxide 6.2 Sodium nitrate 6.1

the solution was made by dissolving:

I G ams Cadmium nitrate tetrahydrate 220 Cadmium oxide 136 Sodium cyanide 410 Sodium hydroxide 40 in distilled water or deionized water, and then making "the final volume 2 litres. v I Example 2 To approximately 350 cc. of distilled or deionized water, add 57.15 grams of finely powdered cadmium oxide and 88.6 grams sodium cyanide. Stir until dissolved, and then add and dissolve 10. grams of potassium hydroxide and 30 grams of potassium nitrates Make up the solution to 500 cc. total volume, and then add and dissolve therein, 0.9 cc. N-amylamine.

Plating may be carried on in this solution, with agitation, over all ranges of normal current densities, oreven as high as 100 a.s.f. without hydrogen embrittlement.

Example 3 Dissolve approximately 200 grains of potassium cadmicyanide in about 800 cc. of distilled or deionized water,- and then add and dissolve about grams of potassium nitrate, 10 grams of potassium cyanide, 10 grams of p0 tassium hydroxide and 0.4 cc. desoxyephedrine. Make the final volume of the solution up to one liter. x

Cadmium plating in this solution may be carried on 'jwithqutembrittlement over a range of current densities varyingbetween approximatcly 10 andx100 a.s.f. Continual agitation is required.

I Example 4 Make a solution containing 8-12% cadmium, by mixing 9.2-13.8% cadmium oxide in pure water, using just sufiicientsodium cyanide to completely dissolve the metallic oxide. Then add about 1% sodium cyanide, about 1% sodium hydroxide, about 5% sodium nitrate, and about 2% by volume of N-aminopropylmorpholine. -With gentle "agitation, cadmium plating from this solution may be carried on over all normal current densities and as high as 72 -a.s.f. without hydrogen embrittlement.

1' 'ExampIeS Prepare a solution containing about l% cadmium by mixing'about 11.5% finely powdered cadmium oxide with distilled or'deionized water and adding just enough sodium cyanide to dissolve the oxide. Then add and dissolve about 1% additional sodium cyanide, 1% sodium hydroxide, and 6% potassium nitrate. I Saturate this solution with di-amylamine by adding about 0.05% by volume and stirring. Filter the solution to remove any haze which may have developed due to undissolved amine. The electroplating of cadmium from this solutionniay be conducted without embrittlement over all usual current densities up to 50 a.s.f., using mild agitation.

"'lThe concentration of the throwing power additive in the solutions may be regulated by choosing an amine which is sparingly soluble-in the plating solution, and saturating the solution with it. The selected amine should be soluble enough to have the desired effect on the throwing power,'and yet should not be sufiiciently soluble to cause embrittlement at any current density normally used in the operation of the baths. Di-n-amyl amine is an example of an additive suitable for this purpose.

It is to be understood that the invention is not to be construed as based upon or dependent upon the theories which we have expressed. Nor is the invention to be regarded as limited to the express procedures or materials set forth, these details being given only by way of illustration and to aid in clarifying the invention. We do not regard such specific details as essential to the invention except insofar as they are expressed by way of limitation in the following claims wherein it is our intention to claim all novelty inherent in the invention as broadly as permissible in view of the prior art.

We claimrj "1'. A 'non-embrittling alkaline cadmicyanide electroplating solution having a cadmium metal content of from 8% to 15% on a weight per unit volume basis and characterized by the inclusion therein of about 1 to 6.5% of a nitrate expressed in terms of sodium nitrate on a weight per unit volume basis and about .1 to (ma weight per unit volume basis of a water soluble aliphatic amine containing from 3 to 8 carbon atoms as a throwing power additive. 1

2. 'A non-embrittling alkaline cadmicyanide electroplating solution characterized by the inclusion therein of. about 1 to 615%: expressed in terms of sodium nitrate on a weight per unit volume basis of a water soluble nitrat'e' and about .1 to 5% 'on a weight per unit volume basis of an aliphatic amine containing three to eight carhon-atoms serving as a throwing power additive.

3. A non-embrittling aqueous cadmicyanide electro plating solution of high cadmium metal content and low free cyanide content containing from approximately 8 to-approximately 15% cadmium metal on a weight per unit volume" basis, from approximately 0.1 to approximately. 3% free sodium cyanide on a weight per unit volume basis, about 1f to 5% on a weight per unit volume basis of -a" water soluble aliphatic amine having a'carboncha'in lengthof'fr'om 3 to 8,'and about"1 to '8- 6.5%expr essed in terms of sodium nitrate'ona weight per unit volume basis of a salt additive selected'froni the group consisting of: i E, f

' Sodium nitrate Potassium nitrate 4.. An aqueous electroplating solution containing on an approximate weight per unit volume basis from '8 to 15% cadmium metalQf rom 15.5 to 21%. total sodium cyanide, from 1 to 6.5% sodium nitrate, and from" 1 to 6 tenths of one percent on a volume basis of a water soluble aliphaticamine containing from 3 to 8 carbon atoms. z

5. An aqueous electroplating solution containing on an approximate weight-per unit volume basis from 8 to 15% cadmium metal, from 15.5 to 21% total sodium cyanide, from" -1 to 6.5% sodium nitrate, from 6 to -8% sodium hydroxide andirom I to 6 tenths otone-percent on a volume basis of awater soluble-' aliphatic amine containing from 3' to-8 carbon atoms. I

6. An electroplating solution containing on an approximate weight perunit volume basis from 8 to 15 cadmium metal, from 15.5 to 21% total sodium cyanide, from 1 to 6.5% sodium nitrate, from 6 to 8% sodium hydroxide, and from 1 to 6 tenths of one percent on a volume basis of at least one throwing power additive selected from the group consisting of:

n-Butylarnine Aniline n-Amylamine Benzylamine n-Hexylamine Beta phenylisopropylamin n-Heptylamine Desoxyephedrine n-Octylamine. ..n Aminopropylmorpholine Cyclohexylamine 1-3 diaminobutane n-Propylamine Di-arnylamine Diethylamine an approximate weight basis 57 grams cadmium oxide,

86 grams sodium cyanide, 10 grams potassium hydroxide, 30 grams potassium nitrate and about 1 cc. n-amylamine' in 500 cc. of solution.

10. An aqueous electroplating solution containing on an approximate weight basis 200 grams potassium cadmi-.

cyanide, 70. grams-potassium nitrate, 10 grams potassium cyanide, 10 grams potassium hydroxide and about 0.4 cc. desoxyephedrine in 1 liter of solution.

11. An aqueous electroplating solution containing on an approximate weight per unit volume basis 8 to 12% cadmium metal obtained by mixing from 9 to 14% cadmium oxide in Water and sufficient sodium cyanide to dissolve the metallic oxide, about 1% sodium cyanide,

about 1% sodium hydroxide, 5% sodium nitrate,- and- I 2% by volume of n-aminopropylmorpholine.

12. An aqueous electroplating solution containing on an approximate weight per unit volume basis about 10% cadmium metal obtained by mixing about 11.5%

powdered cadmium oxide with sufiicient water and sodium cyanide to dissolve the oxide, 1% additional sodium cyanide, 1% sodium hydroxide, 6% potassium nitrate, and 0.05% by volume of di-amylamine.

l3. Anaqueous non-embrittling cadmicyanide electro plating solution containing on a weight per unit volume basis'from'approximately 8 to 15%cadmi'1im' metal,

from approximately 0.1 to approximately 3% free sodium cyanide and from 1 to 6.5 sodium nitrate.

14. An aqueous non-embrittling cadmium electroplating solution containing on an approximate weight per unit volume basis from 8 to 15% cadmium metal, from 15.5 to 21% total sodium cyanide and from 1 to 6.5% sodium nitrate.

15. An aqueous non-embrittling cadmium electroplating solution containing on an approximate weight per unit volume basis 10% cadmium metal, 20.5% sodium cyanide, 6% sodium hydroxide and from 1 to 6.5% sodium nitrate.

16. An aqueous non-embrittling eadmicyanide electroplating solution containing on a weight per unit volume basis from about 8 to about 15% cadmium metal, from about 0.1 to about 3% free sodium cyanide, and from about 1 to 6 /2 of a nitrate expressed in terms of sodium nitrate.

17. An aqueous non-embrittling cadmicyanide electroplating solution containing on a weight per unit volume basis from about 8 to about 15 cadmium metal, from about 0.1 to about 3% free sodium cyanide, and a potassium nitrate content expressed in terms of sodium nitrate of between about 1% and 6 /2 18. An electroplating solution containing on an approximate Weight per unit volume basis from 8 to 15% cadmium metal, from about .1 to about 3% free sodium cyanide, from about 1 to about 6.5 expressed 10 in terms of sodium nitrate of a salt additive selected from the group consisting of:

Sodium nitrate Potassium nitrate and from .1 to 5% of at least one throwing power additive selected from the group consisting of:

n-Butylamine Aniline n-Amylamine Benzylamine n-Hexylamine Beta phenylisopropylamine n-Heptylamine Desoxyephedrine n-Octylamine n-Aminopropylmorpholine Cyclohexylamine 1-3 diaminobutane n-Propylamine Di-amylamine. Diethylamine References Cited in the file of this patent UNITED STATES PATENTS 2,107,806 Soderberg et al. Feb. 6, 1938 2,377,228 Harford May 29, 1945 2,485,565 Chester et al. Oct. 25, 1949 2,838,448 France June 10, 1958 

1. A NON-EMBRITTLING ALKALINE CADMICYANIDE ELECTROPLATING SOLUTION HAVING A CADMIUM METAL CONTENT OF FROM 8% TO 15% ON A WEIGHT PER UNIT VOLUME BASIS AND CHARACTERIZED BY THE INCLUSION THEREIN OF ABOUT 1 TO 6.5% OF A NITRATE EXPRESSED IN TERMS OF SODIUM NITRATE ON A WEIGHT PER UNIT VOLUME BASIS AND ABOUT 1 TO 5% ON A WEIGHT PER UNIT VOLUME BASIS OF A WATER SOLUBLE ALIPHATIC AMINE CONTAINING FROM 3 TO 8 CARBON ATOMS AS A THROWING POWER ADDITIVE.
 16. AN AQUEOUS NON-EMBRITTLING CADMICYANIDE ELECTROPLATING SOLUTION CONTAINING ON A WEIGHT PER UNIT VOLUME BASIS FROM ABOUT 8 TO ABOUT 15% CADMINUM METAL, FROM ABOUT 0.1 TO ABOUT 3% FREE SODIUM CYANIDE, AND FROM ABOUT 1 TO 6 1/2% OF A NITRATE EXPRESSED IN TERMS OF SODIUM NITRATE. 